1. Field of the Invention
The present invention relates to a method and a system for assisting a driver when parking or maneuvering a motor vehicle, which has at least one driver assistance system and a vehicle safety system.
2. Description of the Related Art
Ambience detection sensors are frequently employed in the motor vehicle technology in order to monitor the distance of a motor vehicle from a stationary or movable obstacle such as a pedestrian, e.g. when entering a parking gap, and to indicate to the driver of the motor vehicle the distance from the obstacle optically or audibly, among others, by way of a corresponding display means. Likewise, the distances from the advancing or following traffic participants are monitored when driving rapidly e.g. on a superhighway or when driving slowly in a convoy. For this purpose, radar sensors and/or ultrasonic sensors being components of an ambience detection system that is known to the expert in the art are arranged at the front and/or the rear and on the side in order to monitor a lateral range of the motor vehicle.
Ambience detection sensors are employed in combination with a collision avoidance system, a driver assistance system and/or in a vehicle safety system. Vehicle safety systems can be designed as Electronic Brake System (EBS), Engine Management System (EMS), Anti-lock braking system (ABS), Traction Slip Control (TCS), electronic stability program (ESP), electronic differential lock (EDS), Traction Control System (TCS), electronic brake force distribution (EBD) and/or engine stall torque control (MSR).
Furthermore, the radar system can be a component of a likewise known driver assistance system, for example. Driver assistance systems are implemented as electronic accessory parts in vehicles to assist the driver in defined driving situations. In this regard, safety aspects but predominantly enhancing the driving comfort is frequently in the focus of attention. These systems intervene partly autonomously or autonomously into the drive, control (e.g. accelerator, brake) or signaling devices of the vehicle or warn the driver shortly before or during critical situations by appropriate man-machine interfaces.
Such driver assistance systems are e.g. the parking aid (sensor arrays for obstacle detection and cruise control), brake assistance (BAS), speed control, Adaptive Cruise Control or speed control (ACC), ranging alarm system, turning assist, traffic jam assist, lane tracking system, lane keeping assistance/lane assistance (lane departure warning (LDW)), lane keeping support, lane change assistance, lane change support, Intelligent Speed Adaption (ISA)), Adaptive Swiveling Headlight, tire pressure control system, driver state detection, traffic sign detection, platooning, automatic panic stop (ANB), flashing and dimming assistance for the headlamps, night vision system. More particularly, tire pressure monitoring systems are able to infer directly or indirectly tire pressure loss of the vehicle wheels from the measured angular velocity. Tire pressure monitoring systems are described in the following protective rights, i.e. DE 102005042061 A, DE 19721480 A, DE 1194304 A, EP 1206359A, U.S. Pat. No. 6,826,462A, DE 10032605A, EP 0869875A, EP0675812A, the contents of which are a comprised in the present application.
Furthermore, driver assistance systems assist the driver in the parking maneuver, for example, by finding a suitable initial position for the parking maneuver, presetting an appropriate steering angle or an automatic steering intervention in case the steering motion of the driver is not successful. Besides, systems are in the try-out, which carry out an automatic parking maneuver after having previously measured the parking gap. DE 38 13 083 A1, for example, discloses a system of this type which includes four switches for selecting the type of operation, by way of which the driver can indicate the location and the type of the parking gap. More specifically, the driver selects between left-hand parking gap, left-hand parking space, right-hand parking gap or right-hand parking space.
Furthermore, DE 198 09 416 A1 describes a method of an aided parking maneuver of a motor vehicle and a device for implementing the method, in which an all-around sensor system comprising a great number of distance sensors is used to detect objects in close vicinity of the motor vehicle and their distances from the motor vehicle. A subsequent processing device determines from the distance data the size of a potential parking gap, in case of need the type of its environment, as well as a possible strategy for entering the motor vehicle into the potential parking gap. The strategy found is output by a display device to the driver. The conditions for activating the parking assistance system or the parking assistance function indicated in the prior art method, however, are not appropriate to perform a safe, assisted or automatic parking maneuver.
DE 102005006966 A1 describes a method for parking a vehicle in which a parking path of the vehicle consists of a fixed section in the area of the parking gap and a starting path with a starting point at the fixed section. The starting path which is traveled from an initial position until the starting point is calculated in the form of a polynomial. It must be safeguarded in this regard that the vehicle, starting from the initial position, can be steered with a preset yaw angle onto the fixed section of the parking path or into the parking gap.
To this end, the prior art method especially arranges that the vehicle position, the vehicle yaw angle and the vehicle steering angle is used to find out by means of a characteristic field whether the parking gap can be negotiated from a given initial position. The characteristic field is calculated before (offline) and stored in a control unit within the vehicle. In this arrangement, the yaw angle and the steering angle must be respectively saved in the control unit for a great number of possible initial positions for a parking maneuver.
It is known to steer vehicles automatically along a desired path into a parking gap that has been detected before with the aid of ambient sensors. The desired path is typically predefined in the form of polynomials or as a sequence of circular and clothoid arcs, as has been disclosed e.g. in German published application DE 199 400 7 A1. The parameters of the intended desired path are usually calculated beginning with a starting point.
The methods allowing a parallel parking maneuver in a fully automatic or semi-automatic fashion usually execute this process in the subsequent steps:                1. measuring the parking gap when driving past        2. indicating whether the parking gap is sufficient in size, whether a valid starting range for the parking maneuver was reached        3. calculating a path for entering into the parking gap        4. traveling on the path while simultaneously correcting the path        5. maneuvering within the parking gap.        
In general, the points 1 to 3 are based exclusively on wheel rotational speed sensors and partly on steering angle sensor means, being used to perform an odometry calculation to determine the position, as well as on sensor means laterally measuring the parking gap when driving past.
Point 4 is largely based on this sensor means. This is why it is only possible at the end of the actual travel traversed that the ultrasonic sensors, which are frequently fitted as a standard nowadays, can be employed for a ranging alarm in order to correct the actual travel. Thus, the distances of the ambient sensors directed to the front and to the rear are only available at point 5.
One problem in this procedure can be seen in the major tolerances in tire dimensions, as a result of which differences in travel with equal wheel rotations can develop in spite of DIN standards being observed. In addition, the traveling distances and, thus, the wheel rolling circumferences vary also depending on the depth of profile and inflation pressure during the driving maneuver, what generally takes place in long-term processes. Further inaccuracies develop from errors in the steering angle, e.g. due to play and torsion in the steering drive and the steering linkage, as well as the ambient sensors and their orientation.
It is an object of the invention to provide a method allowing improvement of the determination of a desired path for different driving maneuvers such as parking or ranging maneuvers.